CONTENTS OF VOL. II. XXXIX 



Page. 



B. Shells depressed. Planorbis. Segmentina. . 462 

 Tribe II. Shell eonical. Ancylus. . . 463 



Subdivision II. Body destitute of the protection of a 

 shell. Peronia. . . . ib< 



Class II. Branchifera. 

 Order I. Branchiae external. 



Tribe I. Branchiae exposed. 



A. Branchiae issuing from the cloak dorsally. 



1. Body exposed, and destitute of a shell. 



a. Doris, Polycera. b. Tergipes, Tritonia, Montagua. 



Eolida, Scyllaea, Glaucus, Thethys. . 466 



2. Body concealed in a spiral shell. Valvata. . 472 



B. Branchiae issuing laterally from between the cloak 



and foot. 



1 . Body with a shell. Cyclobranchia. Patella, Chi- 



ton, Chitonellus. . . . 475 



2. Body naked. Inferobranchia. Phyllidia, Diphyl- 



lidia. 476 



Tribe II. Branchiae simple, and concealed when at 

 rest under a lid. Tectibranchia. 



A. Head furnished with tentacula. 



1. Tentacula four in number, a. Aplysia, Notarchus. 



b. Dolabella. . 477 



2. Tentacula two in number. Pleurobranchus. . 480 



B. Head destitute of tentacula. Bulla, Doridium. 483 



Order II. Branchiae Internal. 



Subdivision I. 



Heart entire, and detached from the rectum. 



Tribe I. 



Shell external. 



